Thermal overload switch



. K Sept. 8, 1953 R, E, SEELY 2,651,696.

THERMAL OVERLOAD SWITCH l Filed April 12, 1952 lnvehtor:

Patented Sept. 8, 1953 0F FICE THERMAL YOVERLOAKD SWITCH RichardE`Se`ely,il*`ort Wayne,"Ind., assignor to `General Electric `Company, a-corporation of N ew York .Application April'AlZ, 1952, .'SerialANo.282,031

-1 This invention relates 'to thermal overload switches, "and .moreparticularly to switches of .this type for thermally protecting plural`phase alternating current windings of `motors, alternators,transformers, etc.

In my copending application Serial No. 276,*825, led March .15, 1952 andassignedto the assignee .of the presentapplicatiomitis pointed'out that4in the design of 'three-phase Aalternating current vwindings, v'itisdesirable to provide thermal protection Yfor each phase of thewindings-independently ofthe otheriphases. 'When-the threephasewindings' are lY-connectedy 'it 'is additionally desirable "that thethermal overload device not only be responsive Ato excessivetemperaturein 'each ofthe `three Winding-phases independently of the other phases,`but Valso thatthe device Yopen the circuits 'of the windings bybreaking the 'Y of the Y-'connection- The'above referred toapplicationiurther points `out that Yit is `frequentlyconsidereddesirable inthe'case'of Y-connected three-phase windings toYground'the neutral andit is'there'forealso desirable to provide'thermal lprotection in the vgrounded tneutral Yin `order to' securecomplete lprotection when one :or two of the'power supply lines maybeopened.

larity in the claims annexed to and forming a part of this specication.

This invention in itsbroadest `aspects provides a thermally responsiveelement, such as a bimetallic snap-act'ing disc, having a plurality ofvmovable contacts mounted on one side 'thereof and a Vplurality ofstationary contacts respectively cooperating with the movable contacts.The thermally responsive element is adapted to move from a firststableposition in 'which the contacts are closed into `a second stableposition to open the contacts responsive to a predetermined temperature.Each of'the'stationary contacts-has a heating device, 'such asa heatingre- .sistance connected thereto and arranged inlheattreinstel-.relationship with the thermally'actuated element and on oneside thereof. These Theat- .ing elements are adapted to'berespectivelyconnected in series circuit relation with the Wind- .ings o' .the motor,as described in the abovereerred Ito application. Another heatingdevice, such as a resistance element,;is connected tothe thermallyactuated element and'arranged in heat transfer relationship therewithandonthe other side thereof from the hrst mentioned .heating elements, this'heatingelement'being adapted to .be connected to a ground.

inthe drawing, 'Fig 1 is a cross-sectional view of one embodiment ofthis invention; liig. 2 is a top view of the device of -Fig. 1 with thecover removed; Fig. Slis a fragmentary cross-sectional view oftheimproved thermaloverload switch of Fig. ,1 taken .along the line 3-3 ofFiggl; Fig. i4 is a 'fragmentary .cross-sectional viewof the device of'Fig.l1 showing'the contacts opened; Fig. 45 isa fragmentarycross-sectional view ofainodi'ed form of my improved vthermal overloadswitch; Fig. 6 is a top view of the device 'of Fig. 5

.showingthe coverY partially broken away; Fig. 7 `isa fragmentaryviewof'the bottom o'f the 'device ofFig.l'asseenalongthe lines 1 thereof;

Fig. 8 is a fragmentary cross-sectional view taken schematicillustration showing theconnection of my improved 'thermal overloadswitch with a three-,phase `alternating current motor.

Referring now to Figs. 1, 2, 3, 4, 7 and .58, the improved'therm'aloverload switch of this inventionis shown as comprising the .bodyportionl formed .of suitable insulating material, such as a molded plastic.'The body portion l`has la substantially circular cavity 2 formedHtherein,

'in which the principal elements ofthe device are arranged. The cavity2may be closed bya suitable cover member 3, which maybe secured in anysuitable manner as by screws .1! 4engaging tapped openings 'E formed insuitable bosses A[i onthe'body portion l.

The .essential vcomponent of this device is a bimetallic snap-actingdisc 'i positioned in the cavity '2, substantially Vlliing the openingthereof. The 'bimetallic disc is spaced vfrom the'bottom '8 of thecavity 2 and is supported'by a suitable post member '9 extendingthroughthe lbottom l iof'the bodyportion 1i. A suitable nut 'l l threadinglyengaging threads f2 formed on the postdpermits adjustment of the,operating characteristics of the disc 1.

A'plurality of evenly spaced movable contacts I3 are mounted on theinner side of the disc 'I within the cavity 2. The movable contacts I3cooperate with stationary contacts III within the cavity 2, thestationary contacts Id being spaced from the bottom 8 of the cavity 2and having extension portions I secured to the bottom portion III of thebody portion I. Ears IIIB are formed on the disc 'i and are arranged inrecesses II in the wall of the cavity 2, the stationary contacts I4having their extension portions I5 also ar- 4a second stable position asshown in Fig. 4 into which it moves responsive to a predeterminedtemperature with the contacts I3 and I4 open, a plurality of resistanceheating elements are provided interconnecting the stationary contactsIII and the terminal portions I8. Each of these resistance heatingelements has a first portion 2l secured to the underside of thestationary conf tact I4, as by soldering, and a second portion 22connected to the terminal portion I8 of the diametrically oppositeterminal, with the intermediate portion 23 partially surrounding thepost 9, as most clearly shown in Fig. 3. It is thus seen that theresistance heating elements respectively interconnect the stationarycontacts and the terminals extending downwardly `away from thebimetallic disc 'I. Since these resistance heating elements are arrangedwithin the cavity 2, they thermally affect the disc and whensufficiently heated will cause it to snap into the position shown inFig. 4 to open the contacts I3 and III. y

In order to provide the ground protection, another resistance heatingelement 24 is provided having its end 25 connected to a spring member26. The spring member 28, which is secured to the body portion I bymeans of a mounting member 21 has a portion 28 biased against the headof the bolt 2 which supports the bimetallic disc 'I. Thus, the end 25 ofthe resistance heating element 2li is connected to the disc I while itsend 29 isconnected to another external terminal 30. This terminal issecured to the body portion I outside of the cavity 2 and has anexternal portion SII to which a ground connection may be made.

Referring now to Fig. 9, it is seen that the external terminals I9 areadapted to be connected in series circuit relation with the windingphases 32 of a three-phase alternating current motor 33, the windingphases 32 being connected to a three-phase source of power (not shown)by means of lines 34 and three-pole switch 35. It will also be seen thatthe outer external terminal 3i is adapted to be connected to a ground.It will be readily apparent that the resistance elements in series withthe motor windings are arranged on one side of the bimetallic snapactingdisc 'I while the ground resistance heating element 24 is arranged onthe other side thereof and in a plane parallel with the plane of thedisc. It will thus be readily seen that this device provides protectionof each phase of the ,4 motor winding independently of the other phase,and that complete protection is provided in the event of opening of oneor two of the supply lines by the use of the neutral heating element.General overload protection is, of course, provided uniformly by thephase heaters 23 and the bimetallic disc 1. While a bimetallicsnap-acting disc 'I has been shown, it will be readily understood thatany other suitable bimetallic or heat responsive element could be usedin this construction.

Referring now to Figs. 5 and 6, in which like elements are indicatedwith like reference numerals, it is seen that the heating resistanceelements take the form of coils 36 having their upper ends 3l suitablysecured to the under sides of stationary contacts I4 and their lowerends 3B connected to the upper sides of terminal portions IS. It will bereadily seen that the heating resistance coils 36 are connected betweenadjacent stationary contacts yand terminal portions and that they arearranged vertically with respect to the bimetallic disc l. The neutralresistance heating element 2li is `again arranged on the side of thebimetallic disc 'I remote from the phase heating elements 36 and in aplane parallel with the disc.

Referring now to Fig. '7 which shows a fragmentary view of the bottom ofthe switch of either Figs. 1 or 5, it is shown that a plurality ofmolded ribs 39 formed integral with the bottom III of the body portion Iseparate the external terminals I9 which project from the bottom Ill ofthe body I. Fig. 7 also most clearly illustrates the equal spacing ofthe portions I5 of the stationary terminals III and their arrangement inslots III] in the body portion I. Fig. 8 illustrates the manner ofretaining the terminals and also the stationary contact members in thebody portion, it being seen that the connecting portion 20 between theexternal terminal I9 and the internal portion I8 has a pair ofprojections 4I formed thereon to secure the terminal in position. Theprojecting portions I5 of the stationary contacts III, the connectionportion intermediate the terminal 3| and its connection with the groundresistance heater 24, and the portion 2'I of the mounting member for thespring 26 are also similarly formed.

It will now be readily apparent that this invention provides an improvedthermally actuated overload switch for a plural phase alternatingcurrent winding arranged to provide protection for each winding phase ofthe electrical apparatus in addition to ground protection characterizedby its compact construction. Furthermore, this switch is fast acting byvirtue of the arrangement of the heating resistances in eicient heattransfer relationship with the bimetallic disc and by virtue of the heatas generated by current iiowing through the bimetallic disc.

While I have shown and described particular embodiments of thisinvention, further modications and improvements will occur to thoseskilled in the art. I desire it to be understood, therefore, that thisinvention is not limited to the forms shown and I intend in the appendedclaims to cover all modications which do not 1depart from the spirit andscope of this invenion.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A thermal overload switch for plural phase alternating currentapparatus comprising a bimetallic snap-acting disc having a plurality ofmovable contacts mounted on one side thereof, a plurality of stationarycontacts respectively cooperating with said movable contacts, said dischaving a first stable position with said contacts closed and beingadapted to move into a second stable position to open said contactsresponsive to a predetermined temperature, a plurality of terminalsspaced from said stationary contacts on the side thereof remote fromsaid one side of said disc, a plurality of heating reistance coilsrespectively interconnecting said stationary contacts and said terminalsfor thermally affecting said disc, and another heating resistance havingone end connected to said disc and its other end connected to anotherterminal, said other heating resistance being arranged in heat transferrelationship with the other side of said disc.

2. A thermal overload .switch for plural phase alternating currentapparatus comprising a bimetallic snap-acting disc having a plurality ofmovable contacts mounted on one side thereof, a plurality of stationarycontacts respectively cooperating with said movable contacts, said dischaving a first stable position with said contacts closed and beingadapted to move into a second stable position to open said contactsresponsive to a predetermined temperature, a plurality of terminalsrespectively arranged diametrically opposite said stationary contactsand spaced therefrom on the side thereof remote from said one side ofsaid disc, a plurality of heating resistances respectivelyinterconnecting each of said stationary contacts and the terminaldiametrically opposite therefrom, and another heating resistance havingone end connected to said disc and its other end connected to anotherterminal, said other heating resistance being arranged in heat transferrelationship with the other side of said disc.

3. A thermal overload switch for plural phase alternating currentapparatus comprising a body portion having a cavity formed therein, abimetallic snap-acting disc arranged in said cavity substantiallyfilling the opening thereof and spaced from the bottom thereof defininga compartment, a plurality of movable contacts mounted on the inner sideof said disc in said compartment, a plurality of stationary contactsmounted in said body portion in said compartment and spaced from thebottom thereof, said stationary contacts respectively cooperating withsaid movable contacts, a post in said compartment and mounted on saidbody portion for supporting said disc, a plurality of evenly spacedterminals mounted on said body portion in said compartment adjacent thebottom thereof and spaced from said stationary contacts, said dischaving a first stable position with said contacts closed and beingadapted to move into a second stable position to open said contactsresponsive to a predetermined temperature, each of said stationarycontacts having a heating resistance connected thereto and extending oneof said terminals, said heating resistances being arranged in heattransfer relationship with said one side of said disc, a spring memberarranged on the other side of said disc having one end mounted on saidbody portion and its other end biased against the end of said post andanother heating resistance arranged on said other side of said d discwith one end connected to said other end of said spring member and itsother end connected to another terminal.

4. A thermal overload switch for plural phase alternating currentapparatus comprising a body portion having a cavity formed therein, abimetallic snap-action disc arranged in said cavity substantiallyfilling the opening thereof and spaced from the bottom thereof defininga compartment, a plurality of evenly spaced movable contacts mounted onthe inner side of said disc in said compartment, a plurality of evenlyspaced stationary contacts mounted on said body portion in saidcompartment and spaced from the bottom thereof, said stationary contactsrespectively cooperating with said movable contacts, a post in saidcompartment and mounted on said body portion for supporting said disc, aplurality of evenly spaced terminals mounted on said body portion insaid compartment adjacent the bottom thereof and spaced from saidstationary contacts, a plurality of heating resistances in saidcompartment respectively connecting each of said stationary contacts andthe one of said terminals substantially oppositely disposed therefromfor thermally aiecting said disc, said heating resistances extendingaway from said inner side of said disc toward said bottom of said cavityand having a loop portion partially surrounding said post, and anotherheating resistance having one end connected to the outer side of saiddisc and its other end connected to another terminal mounted on saidbody portion outside of said cavity for thermally affecting said disc.

5. A thermal overload switch for plural phase alternating currentapparatus comprising a body portion having a cavity formed therein, abimetallic snap-action disc arranged in said cavity substantially llingthe opening thereof and spaced from the bottom thereof defining acompartment, a plurality of evenly spaced movable contacts mounted onthe inner side of said disc in said compartment, a plurality of evenlyspaced stationary contacts mounted on said body portion in saidcompartment and spaced from the bottom thereof, said stationary contactsrespectively cooperating with said movable contacts, a post in saidcompartment and mounted on said body portion for supporting said disc, aplurality of evenly spaced terminals mounted on said body portion insaid compartment adjacent the bottom thereof and spaced from saidstationary contacts, a plurality of heating resistance coils in saidcompartment respectively connecting said stationary contacts and saidterminals for thermally affecting said disc, said heating resistancecoils being vertically arranged with respect to said disc, and anotherheating resistance having one end connected to the outer side of saiddisc and its other end connected to another terminal mounted on saidbody portion outside of said cavity for thermally affecting said disc.

RICHARD E. SEELY.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 2,309,207 Newton Jan. 26, 1943 2,414,531 Johns Jan. 21, 1947

